Osmosis and thermodynamics explained by solute blocking
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A solute-blocking model is presented that provides a kinetic explanation of osmosis and ideal solution thermodynamics. It validates a diffusive model of osmosis that is distinct from the traditional convective flow model of osmosis. Osmotic equilibrium occurs when the fraction of water molecules in solution matches the fraction of pure water molecules that have enough energy to overcome the pressure difference. Solute-blocking also provides a kinetic explanation for why Raoult’s law and the other colligative properties depend on the mole fraction (but not the size) of the solute particles, resulting in a novel kinetic explanation for the entropy of mixing and chemical potential of ideal solutions. Some of its novel predictions have been confirmed; others can be tested experimentally or by simulation.
KeywordsOsmosis Thermodynamics Kinetics Aquaporin Colligative properties Controversy
I wish to thank Eileen Clark, Robert Hilborn, Jaqueline Lynch, Philip Schreiner, and the boys for helpful comments on an earlier draft of the manuscript. Support from the National Institutes of Health (Fellowship GM20584) and National Science Foundation (Grant No. 0836833) is gratefully acknowledged.
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